The present invention relates to locks and more particularly to "electronic" locks of the kind comprising means for detecting a code presented to the lock; a bolt retractable by the turning of an associated rotatable member (termed herein "thrower"); and an electromechanical release mechanism which normally blocks turning of the thrower, at least to the extent sufficient to retract the bolt, but which permits such turning in response to the detection of a proper code. The invention is especially concerned with locks of this kind for use where the code is carried by portable tokens shaped to resemble and functionally equivalent to conventional keys (and termed as such throughout this specification) but where the code is borne in a form to be detected by electronic rather than purely mechanical means. The invention may, however, also find utility where the code entry is accomplished by means other than "keys", of which examples are given hereinafter.
Locks of the kind stated are well known, at least in the patent literature, and have been proposed in conjunction with diverse methods of electronic key code detection. Some examples are described in United Kingdom patent applications Nos. 2024922, 2055951, 2139689 and 2166484 and European patent application no. 0293137. In these examples the electromechanical release mechanism invariably comprises a solenoid which is adapted to move an abutment into or out of its blocking position in accordance with the state of energization of the solenoid. A solenoid moving an abutment is not, however, by any means the ideal choice of control element particularly when space and power-consumption are at a premium (as, for example, in the case where the release mechanism is to be run from an associated self-contained battery supply from which a long service life is expected) and an aim of the invention is to provide a lock of the kind stated with a secure and compact release mechanism which is capable of operation with a significantly lower consumption of electrical power than a comparable solenoid-driven mechanism.
From European patent application no. 0228027 there is known an electromechanically-released lock for a safety deposit box where the release mechanism includes a stationary electromagnet rather than a solenoid moving an abutment. The armature for the magnet is carried at one end of a lever which is in turn pivoted to a blocking element for the bolt. A spring normally biases the lever to pivot the armature into contact with the magnet and operation of a handle to withdraw the bolt tends to pivot the lever on the blocking element in the opposite sense. While the magnet is not energized, operation of the handle pivots the armature away from the magnet until movement of the handle is itself blocked by the blocking element. When the magnet is energized, however, the armature is held stationary upon it by magnetic attraction and pivoting of the lever by the handle causes the lever to lift the blocking element to its releasing position, about the fulcrum represented by the armature, against the force of the spring. Although the electromagnet is not required to cause movement of any other element in this mechanism it must apply a substantial attraction force to the armature to resist the forces tending to pivot the armature away during the movement of the blocking element to its release position, and is therefore still likely to consume a significant amount of power. This mechanism may also be susceptible to compromise by manipulation or vibration and will be rendered ineffective to prevent retraction of the bolt if the armature should become stuck to the magnet (e.g. through freezing or by means of a deliberate attack). It is also geometrically unsuited to a lock with a rotary thrower.